Tall vertical scr

ABSTRACT

An exhaust aftertreatment system including an exhaust conduit transmitting exhaust from an engine, a reductant introduction system introducing a reductant into the exhaust, and a selective catalytic reduction catalyst (SCR) receiving the exhaust and reductant. A SCR length divided by a SCR width is greater than 4. A SCR cell density is less than 180 cells per square inch of cross-sectional area of the SCR. The SCR is vertically mounted adjacent a corner of a cab of a machine.

TECHNICAL FIELD

The present disclosure relates to engine exhaust aftertreatment systemsand more particularly to the size, orientation, and locations ofcomponents in exhaust aftertreatment systems.

BACKGROUND

A selective catalytic reduction (SCR) system may be included in anexhaust treatment or aftertreatment system for a power system to removeor reduce nitrous oxide (NOx or NO) emissions coming from the exhaust ofan engine. SCR systems use reductants, such as urea, that are introducedinto the exhaust stream.

U.S. Pat. No. 6,182,443 (the '443 patent) discloses an aftertreatmentsystem including an SCR system. The SCR includes a monolithic structurewith a catalyst applied. The monolithic structure has channels or cellsthrough which the exhaust passes and interacts with the appliedcatalyst. According to the '443 patent, the “[c]ell density should bemaximized consistent with pressure drop limitations and is preferably inthe range of 200-800 cells per square inch of cross-sectional area ofthe structure.”

SUMMARY

The present disclosure provides an exhaust aftertreatment systemincluding an exhaust conduit transmitting exhaust from an engine, areductant introduction system introducing a reductant into the exhaust,and a selective catalytic reduction catalyst (SCR) receiving the exhaustand reductant. In one aspect a SCR length divided by a SCR width isgreater than 4. In another aspect a SCR cell density is less than 180cells per square inch of cross-sectional area of the SCR. In yet anotheraspect the SCR is vertically mounted adjacent a corner of a cab of amachine.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view of a machine including a power system withan engine and an aftertreatment system.

FIG. 2 is a side view of a SCR known in the prior art.

FIG. 3 is a side view of a SCR from FIG. 1.

FIG. 4 is a side view of an alternative SCR from FIG. 1.

FIG. 5 is a cross-sectional view of the alternative SCR from FIG. 3.

FIG. 6 is another cross-sectional view of the alternative SCR from FIG.3.

DETAILED DESCRIPTION

FIG. 1 shows a machine 1 including a cab 2 where an operator 3 sits anda power system 10. The machine 1 might be a tractor (as illustrated),on-highway truck, car, vehicle, off-highway truck, earth movingequipment, material handler, logging machine, compactor, constructionequipment, generator, pump, aerospace application, locomotiveapplication, marine application, or any other device or applicationrequiring a power system 10.

The power system 10 includes an engine 12 and an aftertreatment system14 to treat an exhaust stream 16 produced by the engine 12. The engine12 may include other features not shown, such as controllers, fuelsystems, air systems, cooling systems, peripheries, drivetraincomponents, turbochargers, exhaust gas recirculation systems, etc. Theengine 12 may be any type of engine (internal combustion, gas, diesel,gaseous fuel, natural gas, propane, etc.), may be of any size, with anynumber of cylinders, and in any configuration (“V,” in-line, radial,etc.).

The aftertreatment system 14 includes an engine exhaust conduit 18delivering the exhaust stream 16. The aftertreatment system 14 includesan exhaust conduit 18 and a Selective Catalytic Reduction (SCR) system20. The SCR system 20 includes an SCR 22, and a reductant supply system24.

In some embodiments, the aftertreatment system 14 may also include adiesel oxidation catalyst (DOC) 26, a diesel particulate filter (DPF)28, and a clean-up catalyst 30. The DOC 26, DPF 28, SCR 22, and clean-upcatalyst 30 involve the appropriate catalyst or other material disposedon a substrate. The substrate may consist of cordierite, siliconcarbide, other ceramic, or metal structure. The substrates may form ahoneycomb structure with a plurality of through going channels or cellsfor the exhaust stream 16 to pass through. The DOC 26, DPF 28, SCR 22,and clean-up catalyst 30 substrates may be housed in canisters 31. TheDOC 26 and DPF 28 may be in the same canister 31, as shown, or separate.Likewise, the SCR catalyst 22 and clean-up catalyst 30 may also be inthe same canister 31, as shown, or separate.

The aftertreatment system 14 is configured to remove, collect, orconvert undesired constituents from the exhaust stream 16. The DOC 26oxidizes Carbon Monoxide (CO) and unburnt hydrocarbons (HC) into CarbonDioxide (CO2). The DPF 28 collects particulate matter or soot. The SCRcatalyst 22 is configured to reduce an amount of NOx in the exhauststream 16 in the presence of a reductant.

The clean-up catalyst 30 may embody an ammonia oxidation catalyst(AMOX). The clean-up catalyst 30 is configured to capture, store,oxidize, reduce, and/or convert reductant that may slip past orbreakthrough the SCR catalyst 22. The clean-up catalyst 30 may also beconfigured to capture, store, oxidize, reduce, and/or convert otherconstituents present.

In the illustrated embodiment, the exhaust stream 16 exits the engine12, passes through the DOC 46, DPF 48, then passes through the SCRsystem 20, and then passes through the clean-up catalyst 30 via theexhaust conduit 18. The SCR system 20 is downstream of the DPF 28 andthe DOC 26 is upstream of the DPF 28. The clean-up catalyst 30 isdownstream of the SCR system 20. In other embodiments, these devices maybe arranged in a variety of orders and may be combined together. In oneembodiment, the SCR catalyst 22 may be combined with the DPF 48 with thecatalyst material deposited on the DPF 48. Other exhaust treatmentdevices may also be located upstream, downstream, or within the SCRsystem 20.

The reductant supply system 24 is configured to introduce the reductantin to the exhaust upstream of the SCR 22. The reductant supply system 24may include a reductant source 32, reductant line 34, and an injector36. The reductant supply system 24 may also include a pump and one ormore valves to achieve and control the delivery of the reductant.Reductant may also be provided to the SCR 22 from the engine 12 or in avariety of other ways.

The reductant supply system 24 may also include a thermal managementsystem to thaw frozen reductant, prevent reductant from freezing, orpreventing reductant from overheating. Components of the reductantsupply system 24 may also be insulated to prevent overheating of thereductant. The reductant supply system 24 may also include an air assistsystem for introducing compressed air. The air assist system may also beused to purge the reductant line 34 and other reductant supply system 24components of reductant when not in use.

The injector 36 injects reductant in a mixing section 37 of the exhaustconduit 18 where the reductant may be converted and mix with the exhauststream 16. A mixer may also be included in the mixing section 37 to helpthe conversion and mixing. While other reductants are possible, urea isthe most common reductant. The urea reductant converts, decomposes, orhydrolyzes into ammonia (NH3) and is then adsorbed or otherwise storedin the SCR catalyst 22. The NH3 is then consumed in the SCR Catalyst 22through a reduction of NOx into Nitrogen gas (N2).

A heat source may also be included to remove the soot from or regeneratethe DPF 28, thermally manage the SCR catalyst 22, DOC 26, or clean-upcatalyst 30, to remove sulfur from the DOC 26, DPF 28, or SCR catalyst22, or to remove deposits of reductant that may have formed. The heatsource may embody a burner, hydrocarbon dosing system to create anexothermic reaction on the DOC 46, electric heating element, microwavedevice, or other heat source. The heat source may also embody operatingthe engine 12 under conditions to generate elevated exhaust stream 16temperatures. The heat source may also embody a backpressure valve oranother restriction in the exhaust conduit 18 to cause elevated exhauststream 16 temperatures.

The aftertreatment system 14 may also include a control system with NOXsensors. The control system may use the NOX sensor or engine maps tocontrol the introduction of reductant from the reductant supply system24 to achieve the level of NOX reduction required while controllingammonia slip. The control system may also include soot sensorsassociated with the DPF 28 to control regeneration of the DPF 28.

INDUSTRIAL APPLICABILITY

Emission regulations have only recently necessitated the need for SCRsystems 20. Prior art SCR systems utilize horizontally mounted, shortand wide SCRs 38 with high cell densities, as shown in FIG. 2. The shortand wide dimensions limit backpressure losses while the high celldensities provide high NOX conversion efficiencies by exposing theexhaust to a greater surface area of catalyst material. The horizontalmounting is utilized for structural reasons. Ceramic substrates areoften used which may be heavy, especially when cell densities are high.The horizontal mounting allows the heavy substrate to be supported. Thehorizontal mounting is also conducive to receive the reductant, which isoften injected in a horizontal section of the exhaust pipe.

However, many existing machines 1 were not designed to accommodate ashort and wide SCR 38. The design changes required to accommodate such ashort and wide SCR 38 may impact an operator's 3 visibility. Such designchanges may include larger hoods or engine compartments. Such designchanges are also expensive.

The disclosed SCR 22 is suited to be located in certain mountinglocations of the machine 1. The mounting location may be selected for anumber of different reasons. For example, the mounting location may be alocation where the impact on operator 3 visibility is reduced or alocation where the machine 1 was already designed to have a mufflerlocated. Because an SCR often provides the level of sound dampeningrequired, the SCR 22 may replace the muffler and therefore only limiteddesign changes to the machine 1 would be required

An example of one such mounting location is shown in FIG. 1. FIG. 1shows a tractor with the SCR 22 mounted along or adjacent a corner ofthe cab 2. While adjacent, the SCR 22 may still be spaced apart from thecorner of the cab, which a common location for a muffler. The corner ofthe cab 2 provides the operator 3 with a greater degree of visibilitythan other solutions and is a location where a muffler is commonlylocated.

Many other mounting locations for mounting of the SCR 22 are alsopossible. For example, with a bulldozer or track-type tractor sidevisibility is important and the SCR 22 may be mounted more toward thefront center of the cab 2 over the engine compartment. Other machines,such as motor graders, compactors, excavators, and wheel loaders oftenhave rear-mounted engines so the SCR 22 may be vertically mounted behindthe cab 2. Yet other machines, such as large mining trucks and wheeltractor-scrapers have side-mounted engines so the SCR 22 may bevertically mounted to the side of the cab 2. In another example, themounting location for an on-highway truck may be the back corner of thecab 2, despite a front engine mounted design. The mounting location doesnot necessary require a vertical orientation, for many automotiveapplications the mounting location is a horizontal mounting along thelength and underneath the vehicle.

Many of the mounting locations described above require the SCR not to betoo wide. A wide SCR 38 could limit visibility in vertical mountingsituations outside the cab 2. A wide SCR 38 could also be a clearanceissue in horizontal mounted situations underneath the machine 1.

However, while the mounting locations described above often do notfacilitate a wide SCR 38, they do often allow the SCR 22 to be long. Invertical mounting locations, the SCR 22 may also need to be lightbecause the vertical mounting provides limited support. Meanwhile theSCR 22 must still achieve the level of NOX conversion needed withoutcreating too much backpressure.

FIG. 3 illustrates an SCR 22 configured to meet the needs listed above.The illustrated SCR 22 has a SCR length 40 and a SCR width 42. The SCRwidth 42 may represent a diameter if the SCR 22 is circular. The SCRlength 40 and SCR width 42 establish an aspect ratio of SCR length 40divided by SCR width 42 of greater than 4. In other embodiments theaspect ratio of SCR length 40 divided by SCR width 42 may be greaterthan 3.5. In yet other embodiments the aspect ratio of SCR length 40divided by SCR width 42 may be greater than 5, between 4 and 8, orbetween 5 and 8. By way of comparison, prior art wide SCRs 38, as shownin FIG. 2, may have lower aspect ratios of typically between 1 and 2.

In contrast to the prior art's teachings of higher cell densities, thelong SCR length 40 enables lower cell density and larger cells orchannels. Because of the long SCR length 40, high cell densities are notneeded to create the surface area for exhaust stream 16 contact neededfor high NOX conversion efficiencies. The long SCR length 40 creates thehigh amount of surface area for exhaust stream 16 contact for high NOXconversion efficiencies. The larger cells prevent excessive amounts ofbackpressure created from small cells which block exhaust stream 16flow. The larger cells enable a narrower SCR width 42 while stilllimiting backpressure.

The SCR 22 cell density may be less than 180 cells per square inch ofcross-sectional area. In other embodiments, The SCR 22 cell density maybe between 50 and 180. By way of comparison, prior art wide SCRs 38, asshown in FIG. 2, may have cell densities between 200 and 800 cells persquare inch of cross-sectional area.

The SCR cell density may be a function of SCR length 40 and the powersystem's 10 characteristics. The longer the SCR length 40, the less thecell density may need to be to achieve the desired SCR efficiency. TheSCR length 40 may be between 2 and 8 feet. When the SCR length 40 isbetween 4 and 5 feet the SCR cell density may be between 100 and 150cells per square inch of cross-sectional area. When the SCR length 40 isbetween 5 and 6 feet the SCR cell density may be between 60 and 120cells per square inch of cross-sectional area. When the SCR length 40 isbetween 3 and 4 feet the SCR cell density may be between 130 and 180cells per square inch of cross-sectional area.

The SCR 22 substrate may also be metallic, which is often lighter thanceramic. The lightweight achieved by the low cells per square inch ofcross-sectional area and lighter metallic material helps enable verticalmounting because less weight needs to be supported. The long SCR length40 also helps provide greater surface area between the canister 31 andthe SCR 22 to help achieve the vertical mounting. Metallic substratesmay also be able to be formed in longer structures with through goingcells than ceramic can be extruded into.

A support 44 may also be needed to achieve the vertical mounting. Thesupport 44 may be located underneath the SCR 22 to help support theweight of the SCR 22. The support 44 may be configured to allow theexhaust stream 16 to pass and not block the SCR 22. As seen in FIG. 3,the support 44 may embody tabs or a thin ring welded or otherwisesecured to the inside wall of the canister 31. The support 44 may alsobe thick ring with openings, as seen in FIG. 5. The support 44 couldalso be thin cross-members extending from one side of the canister 31 toanother side.

The reductant mixing section 37 may need to be sufficiently long and mayneed to be horizontal. Spraying a liquid reductant vertically upward maybe problematic due to gravity. In the current configuration the injector36 is mounted horizontal and most of the reductant is gaseous beforeturning vertical to pass through the SCR 22. The reductant mixingsection 37 length allows a majority of the urea reductant to convertinto gaseous ammonia before turning vertical. If the reductant wereinjected in the gaseous form these limitations on the reductant mixingsection 37 could be removed or decreased.

FIGS. 4-6 illustrate a split SCR 50 as an alternative embodiment for theSCR 22 while still achieving the same aspect ratios described above.Unlike the SCR 22 in FIG. 3, the split SCR 50 includes multiple SCR 22bodies with the exhaust stream 16 being split. The split SCR 50 includesan interior SCR 52, exterior SCR 54, exterior passage 56, and aninterior passage 58. The split SCR 50 configuration allows forindividual split SCRs 52 and 54 to have shorter lengths and larger celldensities, like prior art wide SCRs 38.

The interior SCR 52 has a cross-section area that is smaller than thecross-sectional area of the canister 31. The space between the interiorSCR 52 and the canister forms a lower portion 60 of the exterior passage56. An upper portion 62 of the exterior passage 56 widens in atransition zone 64 between the interior and exterior SCRs 52 and 54 tomeet with the exterior SCR 54. The exterior SCR 54 has cross-sectionwith a through-going opening that forms an upper portion 66 of theinterior passage 58. A lower portion 68 of the interior passage 58 matesbetween the interior SCR 52 and the upper portion of the interiorpassage 58 in the transition zone 64. A dividing wall 70 isolates theflow of exhaust in the interior passage 58 from the exterior passage 56in the transition zone 64. The support 44 for the SCR 52 may extendacross yet still allow the exhaust stream 16 to pass through or aroundto enter the lower portion 60 of the exterior passage 56.

A portion of the exhaust stream 16 passes through the interior SCR 52and then through the interior passage 58. The other portion of theexhaust stream 16 passes through the exterior passage 56 and thenthrough the exterior SCR 54. The exhaust stream 16 then exits the splitSCR 50 and may pass through the clean-up catalyst 30.

Others configurations of the split SCR 50 are possible. For example, theorder of interior and exterior SCRs and passages 52, 54, 56, 58 may bereversed. The clean-up catalyst 30 may also be split in a similar manneras the split SCR 50.

Although the embodiments of this disclosure as described herein may beincorporated without departing from the scope of the following claims,it will be apparent to those skilled in the art that variousmodifications and variations can be made. Other embodiments will beapparent to those skilled in the art from consideration of thespecification and practice of the disclosure. It is intended that thespecification and examples be considered as exemplary only, with a truescope being indicated by the following claims and their equivalents.

What is claimed is:
 1. A exhaust aftertreatment system comprising: anexhaust conduit transmitting exhaust from an engine; a reductantintroduction system introducing a reductant into the exhaust; and aselective catalytic reduction catalyst (SCR) receiving the exhaust andreductant, wherein a SCR length divided by a SCR width is greater than4.
 2. The exhaust aftertreatment system of claim 1 wherein the SCRincludes a plurality of cells with a cell density of less than 180 cellsper square inch of cross-sectional area of the SCR.
 3. The exhaustaftertreatment system of claim 1 wherein the SCR includes a plurality ofcells with a cell density of between 130 and 180 cells per square inchof cross-sectional area of the SCR.
 4. The exhaust aftertreatment systemof claim 3 wherein the SCR length is between 3 and 4 feet.
 5. Theexhaust aftertreatment system of claim 1 wherein the SCR is verticallymounted on a machine.
 6. The exhaust aftertreatment system of claim 5wherein the reductant introduction system introduces the reductant intoa horizontal section of the exhaust conduit.
 7. The exhaustaftertreatment system of claim 5 wherein the SCR is mounted adjacent acorner of a cab.
 8. The exhaust aftertreatment system of claim 5 whereinthe SCR includes a metallic substrate.
 9. The exhaust aftertreatmentsystem of claim 5 further including a diesel oxidation catalyst (DOC)and a diesel particulate filter (DPF) upstream of the SCR and a clean-upcatalyst downstream of the SCR.
 10. A exhaust aftertreatment systemcomprising: an exhaust conduit transmitting exhaust from an engine; areductant introduction system introducing a reductant into the exhaust;and a selective catalytic reduction catalyst (SCR) receiving the exhaustand reductant, wherein the SCR includes a plurality of cells with a celldensity of less than 180 cells per square inch of cross-sectional areaof the SCR.
 11. The exhaust aftertreatment system of claim 1 wherein aSCR length divided by a SCR width is greater than
 4. 12. The exhaustaftertreatment system of claim 11 wherein the SCR includes a pluralityof cells with a cell density of between 130 and 180 cells per squareinch of cross-sectional area of the SCR.
 13. The exhaust aftertreatmentsystem of claim 11 wherein the SCR length is between 3 and 4 feet. 14.The exhaust aftertreatment system of claim 11 wherein the SCR isvertically mounted on a machine.
 15. The exhaust aftertreatment systemof claim 14 wherein the reductant introduction system introduces thereductant into a horizontal section of the exhaust conduit.
 16. Theexhaust aftertreatment system of claim 14 wherein the SCR is mountedadjacent a corner of a cab.
 17. The exhaust aftertreatment system ofclaim 14 wherein the SCR includes a metallic substrate.
 18. The exhaustaftertreatment system of claim 14 further including a diesel oxidationcatalyst (DOC) and a diesel particulate filter (DPF) upstream of the SCRand a clean-up catalyst downstream of the SCR.
 19. A machine comprising:an exhaust conduit transmitting exhaust from an engine; a reductantintroduction system introducing a reductant into the exhaust; and aselective catalytic reduction catalyst (SCR) receiving the exhaust andreductant, wherein the SCR is vertically mounted adjacent a corner of acab of the machine.
 20. The exhaust aftertreatment system of claim 19wherein a SCR length divided by a SCR width is greater than 4 and theSCR includes a plurality of cells with a cell density of less than 180cells per square inch of cross-sectional area of the SCR.